B3 – Coarse lime rendering (scrubbed, projected)

Building
Techniques :
B3 – Coarse lime rendering (scrubbed, projected)
Country:
France
PRÉSENTATION
Geographical Influence
Definition
Coarse lime rendering (scrubbed,
projected)
- Protection rendering
- Mixture of lime and sand
- Applied in one, two or three layers
- Use of a trowel
- Coarse aspect, with more or less marked
bumps and gaps
- For modest buildings and secondary fronts
(pinions) of more middle-class constructions
Environment
In France, projected lime rendering is a technique one can find in cities and in the countryside, in all geographical environments: plain, sea side
and mountain.
Its use is common.
Illustrations
General views :
Detail close-up :
Ce projet est financé par le programme MEDA de l'Union Européenne. Les opinions exprimées dans le présent document ne reflètent pas nécessairement la position de l'Union Européenne ou de ses Etats membres.
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B3 France – Coarse lime rendering (scrubbed, projected)
CONSTRUCTION PRINCIPLE
Materials
Illustrations
Binding material - origin and availability (form in which it is available )
In France, for projected lime rendering, the binding material is:
- air lime:
- powder (French denomination: C.L. and D.L.)
- paste, rare because it is badly marketed (Moreover, its realisation is not described in
technical D.T.U. = Documents techniques unifiés = (unified technical data) regulation
bases determining the general conditions for the use of materials)
- natural hydraulic lime powder (French denomination N.H.L.)
Aggregate - origin and availability (form in which it is available )
In France, sand and gravel are the aggregates traditionally used for projected lime rendering.
Aggregate – grading
Worn scrubbed-projected rendering
with thick aggregate
In France, traditionally, projected lime rendering uses coarse sand (unfiltered).
The grading found for sand vary from 2 mm minimum to 6 mm maximum.
Sands one the market are filtered.
Dose ratio for finishing coating
In France, the reported dose ratio for projected lime rendering is:
- 3 volumes of natural hydraulic lime (N.H.L.) for 10 volumes of aggregates;
- 4 volumes of air lime powder (C.L. or D.L.) for 10 volumes of aggregates;
- 2,5 volumes of air lime paste for 10 volumes of aggregates (200 to 250 kg of binding
material for 1 m3 of dry sand).
Tools
In France, the tools for projected lime rendering are a trowel and a hawk used to apply the
coating.
Trades
Trades, Number of workmen necessary
In France, it is very generally the mason who carries out this type of work, or a workman more
specialised in the preparation and application of rendering. Formerly, rather in rural
environment, it this work was frequently carried out by the user himself.
Ce projet est financé par le programme MEDA de l'Union Européenne. Les opinions exprimées dans le présent document ne reflètent pas nécessairement la position de l'Union Européenne ou de ses Etats membres.
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B3 France – Coarse lime rendering (scrubbed, projected)
CONSTRUCTION PRINCIPLE (CONTINUED)
REALISATION DESCRIPTION
In France : (Text in French)
L’enduit à la chaux projeté (jeté-recoupé) est traditionnellement appliqué sur une maçonnerie en pierre brute hourdée.
On ne le rencontre pas sur les maçonneries en pierre taillée équarrie, en pierre taillée 6 faces, en terre crue ou en briques cuites.
La veille de l’application de l’enduit, le support sera parfaitement dépoussiéré et humidifié jusqu’à saturation.
Suivant les conditions atmosphériques et la nature du support, il sera parfois nécessaire de répéter l’opération d’humidification du support juste
avant la mise en œuvre de l’enduit.Le nombre de couches (ou de passes) est très variable.
Il dépend de la régularité de la maçonnerie, du type de jointoiement et du soin apporté à la mise en œuvre de ce type d’enduit.
Traditionnellement, ce type d’enduit minimal pouvait être appliqué en une ou deux couches ; le dosage en liant étant alors de 300 à 350 kg de
chaux pour 1 m3 de sable sec environ.
Actuellement, on pose cet enduit en deux ou trois couches. La première appelée gobetis ou couche d’accrochage est préparée suivant un
dosage de 400 à 450 kg de chaux blanche pour 1 m3 de sable sec grossier. L’épaisseur de cette couche dans les creux sera de 10 mm environ.
Son dressage se fera au nu de la tête des moellons. Le temps de retrait sera de 7 jours pour les enduits à base de chaux hydraulique naturelle et,
suivant les conditions climatiques, d’une à plusieurs semaines pour les enduits à base de chaux aérienne. Un excès d’eau (pluie, le brouillard, ….)
détrempant la maçonnerie empêchera ou ralentira fortement le processus de prise de la chaux.
Le dosage de la couche de finition sera de 200 à 250 kg de chaux blanche pour 1 m3 de sable sec de 3 mm de granulométrie, de préférence.
L’enduit à la chaux sera projeté sur le support au moyen d’une truelle, dressé grossièrement pour l’égaliser et tendre vers une planéité relative en
recoupant avec le côté de la truelle toute la surface couverte. Cette opération s’effectue de bas en haut, en diagonale, de gauche à droite et de
droite à gauche.
Ce projet est financé par le programme MEDA de l'Union Européenne. Les opinions exprimées dans le présent document ne reflètent pas nécessairement la position de l'Union Européenne ou de ses Etats membres.
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B3 France – Coarse lime rendering (scrubbed, projected)
ASPECT, PATHOLOGY
Aspect
Illustrations
Texture, Colour :
In France, the texture of projected lime rendering can be very slightly grainy.
The trowel with which the coating is spread upwards, in diagonal, left to right and right to left,
reveals grains of sand on the surface. These grains are more or less visible according to the
grading and the hand that applies this type of coating.
Colouring depends on the binding material and aggregate used. Sometimes the colour is the
same as the lime paint which is applied as maintenance layer.
Ageing Pathology
Linked to the materials and climatic conditions :
In France, projected lime rendering wears more quickly on the head of the stones, and they
show after a while. This effect is called "rendering with visible stones". It is not a specific
technique but a result of ageing.
Ageing pathology
Stoneheads showing due to wearing in the
more exposed lower parts of the wall
Linked to the technique :
In France, the clogging of grainy textured surface is a quick process in urban environment.
This layer can also fall apart if the support is too smooth.
Maintenance :
In France, projected lime rendering is sometimes maintained with an application of limewash.
USE, EVOLUTION AND TRANSFORMATION
Grained aspect favours the growth of vegetals
Use
Types of buildings :
In France, projected lime rendering is used as minimal protection coating. It is bottom coating
applied before a final finishing. One finds it on the secondary fronts: back annexes, fronts
and pinions.
On a rural building, it can be used on opening frames. It can then quickly be tightened and
painted white to underline the framing or to be smoothed coarsely with a trowel.
Period when the technique appeared / Period of use of the technique –
contemporary or disappeared use
In France, the technique of projected lime rendering is very old.
Still used, but growing scarce.
Reasons of the disappearing or the modification of the technique :
In France, the progressive disappearing of projected lime rendering can be explained by:
•
in the 20th century, multiple processing of facings was given up;
•
unconvincing effectiveness in terms of protection against water of this type of coarse
coating;
•
the grained texture is easily stained and micro-organisms often develop;
•
the fact that the realisation of this technique is not included in French official regulations
(technical D.T.U. 26.1 )
Rem.: the cost of this technique is slightly lower or the same as floated lime.
Ce projet est financé par le programme MEDA de l'Union Européenne. Les opinions exprimées dans le présent document ne reflètent pas nécessairement la position de l'Union Européenne ou de ses Etats membres.
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B3 France – Coarse lime rendering (scrubbed, projected)
USE, EVOLUTION AND TRANSFORMATION (CONTINUED)
Evolution / Transformation
Materials :
In France, the hand-crafted extraction produced coarser sands, more specifically used for projected lime plasters.
Today’s sand grading on the market for lime rendering is generally 2 to 3 mm because these sands are most frequently used for lime scraped or
tightened finishing.
Technical aspects :
In France, lime renderings are quite comparable to projected renderings.
Currently, projected of mortar with fine sand (pneumatic projection pot) and ruler spreading or floated and scraped aspects are different from
projected lime rendering.
Evaluation of materials and techniques of replacement :
In France, " rustic " finishing appeared in the 20th century.
The realisation of these finishings is machine made, with tinted mortars, left bare after projection or partly levelled.
The names of these finishing are not standardised and correspond to catalogue names and trade marks ("scraped ", " rustic ", " crushed ",...).
Ce projet est financé par le programme MEDA de l'Union Européenne. Les o pinions exprimées dans le présent document ne reflètent pas nécessairement la position de l'Union Européenne ou de ses Etats membres.
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